JJ 6L6GCs... WTF?

[Tone Meister]

The JJ6L6s I get from CE Dist are always purchased in matched quads... as I think I previously stated.
In any given month I might buy 6 to 12 sets of quads.
The idle current specs, as measured in the subject amplifiers after power testing for a bit, are always within 2ma or 3ma of each other.
I'm quite satisfied with that.

The problems I have been running into is that the JJ6L6 tubes from CE Dist are almost always unusable because they very quickly become mechanically noisy, rattling, ringing, buzzing and singing away.
It is not a loud noise that comes out of the speaker so much, although those same tubes do have microphonics you can CLEARLY hear right through the power amp stage if you lightly tap the tube, which becomes much worse as time progresses.....but the tubes make their own noise that is quite discerning.
It sounds like all the mica and support structures inside the glass envelope are loose, jangling the glass envelope and the parts are excited in "sympathy" with what ever low to mid tones are going through them.
They radiate their own noise and it sounds like there is something wrong with the amp.
The bad tubes that do rattle badly fail within half the time or less of tubes that do not do this.
I think that is a major defective... CE Dist sells them this way and tells me they do not warranty microphone tubes as they do not consider that a defect.
So, bottom line, I buy many thousands of dollars worth of tubes every year and CE just doesn't get my power tube money anymore.
NONE of the currently purchased Sovtek 6L6WXTs I have been using exhibited any of this damn noise and although not my first choice in tubes, they still sound good and I can ship the amps out with out worrying about a warranty issue on power tubes due to a noise complaint.
As mentioned by a previous participant, I think I will try buying a JJ6L6GC set from Eurotubes at retail and see if they are better in this regard.
If yes, then I will continue to hound CE Dist.

... I'm sad to hear that you're getting low quality matched JJ 6L6GC from CE. that has me worrying about buying a matched sextet from them for my SuperTwin. I do like the low cost at CE, and the thought of buying a sextet at retail isn't all that appealing to me. Does Euro even have a wholesale channel? ...

I've been having the same exact problems with JJ 6L6GC from CE Distribution. Bruce details the issues precisely the way I would have, so there's no reason to restate what has already been said. Going back at least 12 years, I've never had a single problem with tubes I've purchased at Eurotubes, but just like everyone else I prefer the the notion of paying wholesale. If Eurotubes offers wholesale pricing I am unaware of it.

Right now, I have a JJ 6L6GC quad that is completely unusable which were purchased at CE Dist just this week; one is exceptionally microphonic and two more are grossly unstable--current draw is all over the map. They ARE going back, regardless of what CE considers defective, or not.

[Mick Bailey]

I've just had an amp in with hot-switchable EL34s and 6L6s (both sets are fitted). All JJ. The remarkable thing is is how little difference there is between the two, either clean or driven. Very subtle until cranked way too high and even then hardly worth getting excited about. In this context all other factors are the same and both pairs can be used together too. So, from a practical perspective just what characteristics actually differentiate the JJ tube types?

Maybe my cat hears a huge difference.

JJ tubes should be sold with a novelty or toy inside them. At least when they fail (again) you can break them open and have a laugh. Or buy a set of 4 and get a free lemon - yourself.

[Joe L]

I think that negative feedback negates a lot of the differences in the power section. It falls apart then pushing really hard so maybe that's why you hear a difference, however slight, under those conditions.

[bob p]

That's a really good point. The purpose of a functioning NFB loop is eliminate the distortion artifacts that go with gentle overdrive, so I would expect amps that have a "wide" range of function in the NFB loop to sound pretty similar with different tube types, as long as the loop is functioning as intended. I'm thinking that you shouldn't hear a difference between the different tube types while the NFB loop is functioning properly, and that you'd only hear a difference when the NFB loop "fails" at high output levels.

I guess I'm not surprised to hear someone say something that amounts to "all JJ tubes sound the same." I've reached a similar conclusion when subbing non-JJ EL34 for non-JJ 6L6 in my Mesa Mark IV amp that allows power tube type substitutions / mixing, and operation with two different types of tubes at the same time. As long as I'm operating in the linear range of the NFB loop, I'm not hearing any differences between the EL34 and the 6L6 that are worth writing home about. This caused me to give up on the chase of substituting EL34 for 6L6 and/or blending tube types. For years I've just run the amp with only 6L6 and not bothered with mixing tube types.

When I read Mick's latest post (#92) I'm tempted to assume that all JJ tubes sound the same, and to jump to the conclusion that the reason for this is that they all have the same guts in them, that they really are all the same, and that the differentiation between one JJ tube type and another amounts to little more than the name that they stick on the same guts when they put them in a different bottle. As Joe suggests, another conclusion that could be drawn is that the tubes sound the same because a functioning NFB loop makes that happen.

Maybe the best way to assess the differences between different model numbers of tubes is to use an amp that has no NFB. doing that would remove one huge variable that's intended to confound the issue.

[Joe L]

Maybe the best way to assess the differences between different model numbers of tubes is to use an amp that has no NFB. doing that would remove one huge variable that's intended to confound the issue.

That is exactly the direction I've been going in lately since building some Marshall 18s and a 36 watt version which use no feedback. You really can hear the difference between output tubes and transformers with no feedback. The transformers make a huge difference with the worse that I've tried being terrible and the best - epic!

And don't forget frequency response and damping factor. Feedback flattens the response dramatically and (don't quote me on this) also lowers the output impedance which tightens the bass response.

Bob, it sounds like we might be on to something here.

[JoeM]

Some discussion on NFB here:

http://music-electronics-forum.com/t13206/

[Joe L]

Thank you Joe! I knew I read the facts of that topic somewhere but without a source that I can easily refer to, I'm hesitant to spout "internet wisdom". I'm pretty sure my friend Randy Aiken was my source for feedback lowering output impedance.

[Mick Bailey]

Out of interest, here's a couple of pics of the amp. Unusual construction.



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[Tone Meister]

I just discovered that right here in my back yard Mojotone offers JJs that are burned in and then matched for the same price CE Distribution is charging (dealer pricing). I am going to take a chance and try a quad to replaces these I have here.

[km6xz]

I forgot about this thread that was in developing interesting directions. I was asked a question regarding setting different tubes at the same idle current, and finding the amplifiers sound different. Yes, I would expect that, they have different electrical properties so would contribute a different transfer function. But what if the circuit that supports the tube was optimized in each case of tube choice, would they "sound" very different. I would not expect a difference that would be noticeable when in a sea of variables that tend to swamp and contributions of tubes to sonic characteristics.
So it is perfectly valid to find a tube type they you like how you exact amp interacts with a particular make or production run of a tube, because the electrical properties of that tube fits the amp electrical properties to result in a transfer function you like. But that says nothing about that same tube's interaction with another amp or different B+ or degree of NFB.

So the often heard claims by marketers and on forums is "EH has too bright top" or "Mullard is fuller in the mids with thinner bottom and nice shimmer in the top" is enough to discount that poster's opinions on anything, not just tubes. If you like the interaction of your amp(not just your model but your exact unit) with a particular batch of tubes, by all means it is fine to say how much you like the combination but you would be getting off into hoodie-voodie land to say that tone will result from that tube put into any other circuit without the same electrical properties. That attribution of sonic characteristics belonging to the tube is where I get suspicious.
If the tubes had some common set of electrical properties, a general recommendation for a type of sound, could be made for specific models of amps but even from the same production line, tube parameters vary over too wide a range to be overly confident that the next set of the same brand will impress you as much.
Circuit topography and conditions have all the difference in the world in sonic performance.
Taking any sort of preferred type of tube such as beam power, triode, or Pentode, for example if you uncovered a lifetime's supply for free, you should be able to design a circuit to get the tone you want, even if those same tubes were poor in some other design.
You can save a lot of headache in chasing tone by increasing negative feedback so a wide variety of off the shelf tubes will sound the same. Amps do overload differently, mostly based on power supply parameters and how the driver handles the wild change in load when the power tube grids start pulling current.
One consideration that is not talked that much about is how the nominal parameters of any electrical device changes when abused, either instantaneously or by accumulation of abuse. Tube guitar amps often do not sound as desired until operating far outside of the components intended operating conditions. There is little difference in tube, transformers and capacitors within their design range of conditions. A transformer performs very differently when there is core saturation but is not part of the spec sheet for it as an example.

[überfuzz]

Off topic! (No JJs in this post)

I see some posts about tone etc in different tubes and shit. Last week I did some service on a bass amp. The owner was pleased, said the new tubes made his pants flutter. Well , I'm writing just so that all ya know that that's the term I'm going to use hereon.

[überfuzz]

Double post

[Tone Meister]

I just discovered that right here in my back yard Mojotone offers JJs that are burned in and then matched for the same price CE Distribution is charging (dealer pricing). I am going to take a chance and try a quad to replaces these I have here.

OK, so far so good. I've tried some pairs and a quad of JJ 6L6GCs from Mojotone and so far no issues. According to the person with whom I spoke on the phone, tubes are pre-screened, burned in, and then matched. So far, after two pairs and a quad life seems good. Each pair and the quad were matched to within 2 mA.

FWIW: I just sent a problematic quad back to CE Dist for a full refund, including my shipping. They balked hard, attempting to key on the word "microphonic" but one tube actually screamed and two drew excessive current as opposed to the other two in the quad. Specifically, there was nearly a 20 mA difference in current draw within the "matched quad"

[Tone Meister]

Ironically, Mojotone buys its tubes from CE Distribution, according to Victoria in CE Dist Service. Where the differences lie, however, are that Mojotone 1) pre-screens and burns in its tubes as part of its matching process, while CE Dist charges extra to burn in tubes and 2) Mojotone sells its pre-screened, burned in, and matched sets for the same exact price as CE Dist.

Add in the fact that I can get parts and tubes in one day from Mojotone versus 3-5 days from CE Dist and what we have is a irrefutable no-shitter folks.

[bob p]

> ... said the new tubes made his pants flutter

amps that move enough air to flutter your pants ... that's a common compliment over at talkbass.